The term broadband covers a host of new products, technologies, services, and networks. One way to define broadbank networks is to categorize them as those networks that support services requiring bit rates well above one megabits per second. Business and residential subscribers will be connected to broadband networks via a common access, operating at 150 megabits per second or above, that can handle a range of different broadband service types. ATM (asynchronous transfer mode) has been chosen as the communication principle on which broadband networks will be based. A furture broadband ISDN (integrated services digital network) will offer the flexibility needed to handle diverse services ranging from basic telephone service to high speed data transfer, videotelephony, and high quality television distribution. The key to this flexibility is ATM which carries digital information in special cells. This allows the network to be used efficiently by applications and services with widely differing bandwidth requirements and call characteristics.
An ATM switching architecture for broadband packet networks referred to as an open-loop shuffleout architecture (FIG. 40) is disclosed in a paper by M. Decina et al., entitled, "Shuffle Interconnection Networks with Deflection Routing for ATM Switching: the Open-Loop Shuffleout", Proc. of 13th International Teletraffic Congress, Copenhagen, June 1991. In the shuffle-out system, the interconnection network is a multistage structure built out of unbuffered 2.times.4 switching elements. Shuffleout is basically an output-queued architecture in which the number of cells that can be concurrently switched from the inlets to each output queue equals the number of stages in the interconnection network. The switching element performs the cell self-routing adoptding a shortest path algorithm which, in case of conflict for interstage links, is coupled with deflection routing. The term open-loop shuffleout is used since the cells that cross the interconnection network without entering the addressed output queues are lost rather than being looped back to the network inputs. Two links are provided from each switching element directly to two of the output queues. The total number of direct links is given by LS, where L is the number of network input ports and S is the number of network stages. For a reasonably large network, however, the number of direct links to output queues becomes excessively large making network implementation very difficult. For example, with L=1024 and S=20, the number of direct links to output queues is 20, 480.
A high performance, self-routing ATM switch, referred to as a rerouting network (FIG. 39) is disclosed in a paper by S. Urushidani entitled, "Rerouting Network: A High-Performance Self-Routing Switch for B-ISDN", IEEE Journal on Selected Areas in Communications, Vol. 9, No. 8, October 1991. The performance of the disclosed ATM switch is enhanced by a "rerouting" algorithm applied to a particular multistage interconnection algorithm. The interconnection algorithm offers many access points to the output and resolves output contention by including buffers at each switching stage. The rerouting network is a multistage interconnection network with more than log.sub.2 L switching stages. The stages are interconnected by routing links and bypass links. The algorithm is applied to embed plural banyan networks within the switch. That is, the partial networks composed of switching elements and routing links from switching stages 1 to 4, from 2 to 5, and so on are banyan networks, because a single path always exists between all input-output pairs. Therefore, a cell that fails to take its desired route due to cell contention at a given stage can restart its routing from the next stage through a banyan network formed in the following log.sub.2 L stages. This restart is referred to as "rerouting". On the other hand, the bypass links route the cell, having reached its destination, to the output line without switching at each switching element. Although the rerouting network has good performance--for example, relatively low blocking--the rerouting network nodes each must include sufficient buffers to store full 53-byte ATM cells for later transmission. Accordingly, the nodes are complex and expensive.
In addition to the above problems, the disclosed shuffleout and rerouting networks also have the significant disadvantages of all large, electronic networks relating, for example, to interconnection bandwidth and density, power dissipation and thermal management, signal cross talk, distortion and dispersion, impedance matching, signal and clock skew, and electromagnetic interference.